Mount St. Helen is Heating Up for an Eruption Again

Washington (HDW) November 10, 2004 – The U.S. Geological Survey (USGS) reported yesterday that growth of a new lava dome inside the crater of Mount St. Helens continued, and is being accompanied by intermittent emissions of steam and ash. As long as this eruption is in progress, episodic changes in the level of activity can occur over days, weeks, or even months. Increase in the intensity of eruption could occur suddenly or with very little warning and may include explosive events that produce hazardous conditions within several miles of the volcano. The picture above, obtained by the USGS, shows the smoke rising from the red molten lava within this powerful volcano.

Small volcanic debris flows could suddenly descend the Toutle River valley if triggered by heavy rain or by interaction of hot rocks with snow or glacier ice. These lahars pose a negligible hazard below the Sediment Retention Structure (SRS) but could pose a hazard to people along the river channel upstream of the SRS. At this time of year, it is not unusual for rivers draining the volcano to contain high concentrations of sediment that turn the water murky.

Although considered less likely at this time, the current eruptive activity could evolve into a more explosive phase that affects areas farther from the volcano and sends significant ash thousands of feet above the crater where it could be a hazard to aircraft and to downwind communities. Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), coupled with eruption models, show that ash clouds that rise above the crater rim today would drift northward to northeastward depending on their altitude. This morning’s images on the VolcanoCam show that a steam plume is rising passively and drifting northward out of the crater. The plume occasionally contains minor ash, which falls out in the crater and on the flank of the volcano, darkening the snow.

Seismic activity remains at a low level compared to that observed early in this unrest. The current seismic activity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismic activity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.

According to the USGS. the latest estimate of the volume of the uplifted area and new lava dome from detailed analysis of aerial photographs taken on 4 November is about 20 million cubic meters (26 million cubic yards). This compares with volumes of about 5 million cubic meters on 4 October and 12 million cubic meters on 13 October. The apparent decrease in rate of volume change (7 million cubic meters in the earlier 9-day period versus 8 million cubic meters in the later 22-day period) doesn’t take into account millions of cubic meters of glacier ice that have been removed from a large part of the area of uplift. Work is underway to assess this effect. The 20-million-cubic-meter volume of the new uplift and lava dome is now more than 25% of the volume of the lava dome that grew in the crater between 1980 and 1986.